1. Technical Field
The present invention relates to safety injectors and, more particularly, to an automatically retractable safety injector and a plunger combination which is one-hand operatable and functions for automatically retracting a needle thereof after the injection is completed to prevent needlestick injury.
2. Description of Related Art
For purposes of avoiding the risk of cross-infection of infectious disease such as AIDS, Hepatitis B, and Hepatitis C; precluding drug addicts from repeatedly using injectors; and protecting medical staff from being accidentally injured by used needles. There are many patents related to so called “safety syringe”. However, most of such safety syringes are designed to be operated with two hands which is not easy and convenient for healthcare worker to use. Even with one hand, the user has to exert a force thereon during injection operation in a way that the syringe requires holding at a specific angle. Consequently, the two-handed operated safety syringes are not preferred by the healthcare works, because there are more risks of needlestick injury than one-handed operated safety syringe.
With attempts to mend the aforementioned problem, Taiwan Patent Publication Number 520995, which is entitled as “Automatically Retractable Safety Injector” and U.S. Pat. No. 6,712,793 B1, which is entitled as “Needle Guard Assembly for the Needle of A Syringe Body”, each suggests a novel and one-hand operatable safe syringe. As shown in FIGS. 1A and 1B, the syringe of prior arts comprises a hollow barrel 12′, a needle hub 11′ for engaging a needle 10′, an annular retracting spring 13′ and a breakable retracting plunger 14′. Therein, the breakable retracting plunger 14′ including a proximal part 17′, a breakable connection 18′, and a hollow distal part 19′, which are formed integrally as one piece. After the breakable retracting plunger 14′ is assembled into the hollow barrel 12′ and used to perform liquid-drug injection operation by a user, the user can continue pushing the breakable retracting plunger 14′ toward the needle 10′ to break the breakable connection 18′, so that the proximal part 17′ can retract into the hollow distal part 19′. As a result, space in the hollow barrel 12′ can be partially spared such that the needle hub 11′ can lead the used needle 10′ to be accommodated in the hollow barrel 12′ together.
However, to facilitate users' exerting force and ensure practicability of the above-mentioned breakable retracting plunger, there are strict requests for symmetry and precision of the breakable connection of the plunger. Consequently, the dimensional tolerance for the molds used to form the one-piece plunger through injection molding process is very small. Besides, the conventional plunger is liable to be broken during fabrication and transportation. Therefore, the yield rate and output are significantly limited while the costs of molds are unavoidably high. Further, with the precise design, safety function of retraction of such conventional plunger can only be effective when the plunger is operated at a predetermined force-exerting angle. Thus, when the prior syringe is implemented to inject a patient at his/her curved-contour skin portion or his/her delicate apparatus, such as the head, postauricular, eyes, or oral skin, it is difficult for a medical staff member to operate the syringe with his/her single hand. Moreover, clumsy operation due to the limited force-exerting angle can accidentally damage the syringe and cause discomfort to the patient.